
		\centering
		\begin{tikzpicture}
			
			% 同一个父亲的孩子锚定点间的距离 层间距离
			\begin{scope}[sibling distance=10pt, level distance=38pt] 
				\Tree[.\node(a1){S};
				[.\node(b1){a};]
				[.\node(b2){A};
				[.\node(c1){S};
				[.\node(d1){b};]    
				]
				[.\node(c2){b};]
				]
				[.\node(b3){e};]
				[.\node(b4){B};
				[.\node(c3){a};]
				[.\node(c4){A};
				[.\node(d2){e};]
				]
				]
				]
			\end{scope}
			
			\node(point1) at ([xshift=-6em,yshift=0em]a1.west){\ding{172}};
			\node(point2) at ([xshift=0em,yshift=-3em]point1.south){\ding{173}};
			\node(point3) at ([xshift=0em,yshift=-3em]point2.south){\ding{174}};
			\node(point4) at ([xshift=0em,yshift=-2.6em]point3.south){\ding{175}};
			
		\end{tikzpicture}
		% \caption{赋值语句b:=a+2 * 5的语法树}

